Automated institutional and industrial spray washing machines are generally configured to embody at least one wash tank or reservoir for maintaining a readily available supply of detergent solution for use by the washing machine. During operation, the washing machine repeatedly draws upon or reuses the detergent solution within the wash tank reservoir, over a period of time (e.g. such as over an entire day), until it is replenished by a fresh solution. During normal useage a part or all of the rinse water is diverted to the wash tank reservoir and a certain amount of the detergent solution is drained off via a stand pipe (for example, in warewashing applications, with food particles and grease), to keep the remaining solution as clean as possible. The proper reservoir solution level may also be maintained by adding water to the reservoir, which reduces or dilutes the detergent concentration of the reservoir solution. Accordingly, to maintain the reservoir solution at the desired detergent concentration level required for proper cleaning, concentrated detergent solution is periodically added to the reservoir by auxiliary detergent dispenser apparatus.
In commercial institutional and industrial washing applications, it is advantageous, from time, cost and safety considerations for operators to be required to only periodically change the washing machine (or its detergent dispenser) with its required detergent--say, for example, only once during the normal working day. Accordingly, the detergent dispenser apparatus used for replenishing the wash tank solution have typically been designed to hold sizable amounts of detergent, and for automatic or semi-automatic operation. Such use of automated detergent dispensers eliminates the need of constant operator attention to the status of the reservoir solution, minimizes operator errors due to operator misjudgment in timing or in the amount of detergent to be added to the reservoir, and provides greater accuracy in maintaining the actual concentration level of the detergent solution within the reservoir.
The supplying or replenishing of concentrated detergent solution to the wash tank reservoir may be performed on a "demand" basis, whereby the detergent concentration level within the wash tank reservoir is monitored by a conductivity cell which typically forms part of an electrical bridge or sensor circuit connected to control emissions of concentrated detergent solution from the detergent dispenser. Alternatively, the dispenser may be hydraulically linked to the wash tank, for example, by a by-pass line from the rinse line of the washer apparatus; with such a by-pass line, each time a rinse cycle of the washing apparatus is executed, the detergent dispenser is activated, dispensing to the wash tank reservoir an amount of concentrated detergent solution in pre-determined proportion to the volume of rinse water used. Since the rinse water is generally diverted to the wash tank, the combined effects of dilution by the rinse water and enrichment by the concentrated detergent solution typically maintains the desired detergent concentration. Alternatively a by-pass from the wash pump manifold may also be connected to the dispenser, for example, when the "demand" basis is employed.
Such solid detergent dispensers of the prior art have used a number of different techniques for converting solid detergent into concentrated detergent solution. The majority of such devices have been designed to convert solid detergent from its "powdered" form. The modes of operation of such dispensers depends somewhat upon the type of washing apparatus with which such dispensers are used, and upon the volume of washing performed by the wash machine apparatus over any given period of time. For example, in large, heavy washing commercial applications, the detergent dispenser may be remotely located (usually in a different physical location) from the washing apparatus and may be configured to convey the solid detergent directly from its shipping container (see for example U.S. Pat. No. 3,595,438, issued July 27, 1971 to Daley, et al and 4,020,865, issued May 3, 1977 to Moffat et al). Dispensers of this type usually have self-contained reservoirs for maintaining a supply of concentrated detergent solution produced thereby, and a pump for transferring on demand, the concentrated detergent solution to the primary wash tank reservoir of the washing apparatus proper. For lower volume commercial washing applications, it is more advantageous to use smaller detergent dispensers configured for mounting to or directly adjacent a washing machine proper. Such dispensers hold relatively smaller amounts of detergent, but offer the flexibility of being immediately accessable for loading by an operator of the washing apparatus, and are thus generally more versatile in their application, than are the larger remotely located dispensers, (see for example, U.S. Pat. No. 4,063,663, issued Dec. 20, 1977 to Larson et al). These dispensers are generally loaded from the top, and directly supply the adjacent washing apparatus reservoir with their produced detergent solution by gravity feed, thus eliminating the need and expense for pumps, while providing an added dimension of reliability. It will be understood that the below-described prior art techniques used for converting solid detergent to concentrated liquid detergent, apply both to the large, remotely located, self-contained reservoir dispensers as well as to the smaller, wall or wash machine mounted, direct gravity feed types of dispensers.
One detergent dispenser technique for converting powdered detergent, is the so-called "water-in-reservoir" type. In the water-in-reservoir dispenser, the powdered detergent is completely submerged under an aqueous solution in a holding tank or pot of the dispenser. A stand-pipe, usually located near the center of the dispenser tank, maintains a constant water/solution level within the dispenser tank. As water is added to the dispenser tank, a concentrated, saturated detergent solution or slurry is formed by the swirling action or agitation of the powdered detergent by the injected water. The added water also causes a portion of the saturated solution in the pot to flow into the stand-pipe, which is connected to supply the wash tank reservoir of the washing apparatus. Since the powdered detergent is always saturated in the water-in-reservoir type of dispenser, the concentration level of the detergent solution produced by such a dispenser over a period of time can significantly vary as the detergent within the dispenser pot is diluted. Further, such techniques are not practical for use with powdered detergents containing active chlorine, since most of the chlorine contained in such detergents is quickly lost through decomposition once the detergent is wetted. Further, there may be safety hazards involved with use of such dispensers if the operator does not carefully follow directions when charging the dispenser. Charging or recharging of such dispensers requires an operator to pour powdered detergent directly into the standing water of the dispenser tank or pot. If highly caustic containing detergent compounds are added too rapidly or in excessive quantities to the dispenser pot, the heat of hydration may cause the solution to boil and spatter. Since the water-in-reservoir type of dispensers are typically mounted above the washing apparatus, at eye level or higher with respect to the operator, such boiling and spattering may pose a danger of caustic splash or spray to the eyes or face of the operator.
Another technique for converting powdered detergent into concentrated liquid detergent, involves the technique of placing the powdered detergent over an inverted curved (usually conically or hemispherically shaped) screen having a mesh size smaller then the powdered detergent particles supported thereby. That powdered detergent which directly overlies the support screen is dissolved as needed, by a fine mist spray from a nozzle disposed below the screen. The concentrated detergent solution formed by the spray falls by gravity into an underlying reservoir, or is directed by a conduit to the wash tank reservoir of the washing apparatus. This technique solves many of the practical and safety problems associated with the water-in-reservoir type of dispenser, since the entire charge of powdered detergent is not wetted, since the solution produced is of more uniform concentration, and since an operator loading the detergent into the dispenser is not subjected to boil-over or spattering of highly caustic detergent solution. Examples of such detergent dispensers used in high-volume applications, wherein the dispenser is generally remotely located from the washing machine apparatus, and wherein the powdered detergent is converted directly from its shipping container, can be found in U.S. Pat. Nos. 3,545,438, issued July 27, 1971 (Daley) and 4,020,865, issued May 3, 1977 Moffat et al). An example of such a detergent dispenser for smaller volume applications, wherein the dispenser is mounted to or adjacent the washing machine apparatus is found in U.S. Pat. No. 4,063,663, issued Dec. 20, 1977 (Larson et al).
While the powdered detergent dispensers such as described by the Daley, Moffat and Larson patents have represented significant contributions to the art of detergent dispensing, the use of solid detergent in powdered form has a number of drawbacks in commercial applications. Due to increased sanitary standards and demands for shorter wash times, recently developed powdered detergents have relatively more complex detergent compositions that are more hazardous to the user, less stable and more difficult to dissolve in a satisfactorily uniform manner. For a detailed discussion of such problems, see the related U.S. patent application Ser. No. 875,784, filed Feb. 7, 1978 (Fernholz et al). Powdered detergents dissolve generally readily because of their high specific surface areas. However, when such powdered detergents include a mixture of a number of components having relatively different dissolving times, such detergents are susceptible to differential solubility problems in automatic detergent dispensers, depending upon the rate of dispensing or the residence (dwell) time of contact between the detergent powder and the dissolving liquid. Those particles having the greatest rate of solubility as well as the greatest specific surface tend to dissolve first, whereas those having the least specific surface and/or the lowest solubility rate tend to dissolve relatively slower. Another problem with powdered detergents relates to possible incompatibility of those constituent components or particles required in the make-up of the detergent so as to perform the required washing function. This problem is particularly acute with those detergents required to contain an active chlorine source and an organic defoamer. The problem associated with such detergents is that there is a substantial loss of available chlorine from such detergents in a relatively short period of time, due to the instability of the chlorine component. The chlorine instability problem is even more acute with high alkalinity powdered detergents because many defoamers and chlorine-containing components are not stable in the presence of highly alkyline chemicals such as sodium hydroxide.
Another problem inherent with powdered detergent, if its components are of different particle sizes and densities, is segregation of those constituent particles during manufacturing, shipping and handling. Even when uniform distribution can be achieved during manufacture, subsequent shipping and handling may cause segregation, leading to non-uniformity in the composition of the detergent when it is withdrawn from the container. Besides the inherent "physical" problems associated with powdered detergents, they are also subject to user misuse and possible abuse, due to user inefficiency, carelessness, or negligence. For example, due to their powdered form, such detergents are often misused for purposes for which they were not designed, and in applications wherein they may present safety problems to the user. Another disadvantage of powdered detergents when handled in bulk form is that they are quite susceptible to spillage onto the floor, on the washing machine, etc. by the user. Also, as previously mentioned with respect to the water-in-reservoir type of dispenser, if such powdered detergents are added too quickly or in excessive quantities to the reservoir tank of such dispensers, they may present safety hazards to the user due to boil-over and spattering.
Another form of solid detergent is the "briquette" form, comprising pre-shaped briquettes of solid detergent. Dispensing systems for dissolving detergent briquettes are known in the art. See, for example, U.S. Pat. Nos. 2,382,163, 2,382,164 and 2,382,165 all issued Aug. 14, 1945 to MacMahon, and U.S. Pat. No. 2,412,819, issued Dec. 17, 1946 to MacMahon. In those prior art systems, the detergent briquettes are dispensed from a modified water-in-reservoir pot-shaped dispenser wherein a number of the briquettes are held in a mesh basket forming a slot across the diameter of the pot. A stream of water directed against the lowermost briquette, in combination with the swirling action of water engaging the submerged portion of the lower-most briquettes provides the dissolving action. The primary advantage of using detergent briquettes in such dispensers is that the user can visually determine when the detergent dispenser reservoir needs a replenishing charge of detergent. As with the water-in-reservoir type of dispenser, however, water is left standing in the reservoir, and a portion of the briquettes are submerged within that water. Accordingly, where there are incompatible components within the detergent briquettes, there can be undesirable interaction therebetween. Further, if the detergent contains a defoamer, that defoamer tends to float to the top of the reservoir during periods of inactivity, forming a slag at the water surface. For these and other reasons, the briquette detergent approach has not attained that degree of commercial success in the conventional institutional and industrial washing machine art, as has the powdered detergent dispensing approach.
The present invention overcomes many of the above-mentioned shortcomings of prior art liquid, powdered and briquette type detergent dispensers. The dispenser apparatus of the present invention provides a concentrated detergent solution for use by washing machines (either of the type remotely located or the type located on or immediately adjacent the dispenser) by proportionately dissolving as needed, solid block-type detergent compositions such as solid-cast detergents, detergent cakes and other solid detergents having significant geometric volume. The dispenser apparatus of the present invention provides a simple, efficient, non-hazardous and reliable technique for producing highly concentrated detergent solution either on a demand basis or by the hydraulically linked by-pass method. The concentrated detergent solution produced by the dispenser of this invention is substantially uniform throughout the conversion of the entire block of solid detergent, and the detergent charge can be rapidly and safely replaced by the user.